404 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



SOUTHERN FIELD-CROP INSECT INVESTIGATIONS. 



Dr. W. D. Hunter has been in charge of these investigations as 

 formerly. 



Cotton boll weevil. — The principal activities have centered 

 around the study and further improvement of the calcium arsenate 

 dusting method of boll-weevil control. Severe weevil infestation 

 in 1922 caused a more extensive commercial use of this method than, 

 ever before. A special study was made of the results secured by 

 api^roximately 1,100 farmers, who dusted altogether 125,485 acres of 

 cotton. These farms were quite uniformly distributed over practi- 

 cally all of the cotton States and represented every type of condition, 

 under which dusting was conducted. A summary shows that slightly 

 over 96 per cent were successful in controlling the weevil to the ex- 

 tent of making the operation profitable. The average increase in 

 yield upon these farms was 339 pounds of seed cotton per acre. The 

 average cost of the season's application was $4 per acre. 



The increase in the use of calcium arsenate developed a shortage 

 of this material. This resulted in the appointment of a committee 

 from various Federal agencies, such as the Geological Survey, Bu- 

 reau of Mines, Bureau of Chemistry, and Bureau of Entomology, as 

 well as representatives of producers and consumers of arsenic in 

 various lines, for a thorough study of the calcium arsenate situation. 

 Undoubtedly such broad consideration of all angles of the problem 

 of arsenic supply and demand Avill do much to stabilize further 

 development and to make supplies available for the farmer as 

 needed. 



Special studies have been conducted along the line of determining 

 the minimum yield per acre upon land where dusting with calcium 

 arsenate would be justified by results obtained. Approximately 

 1,000 tests affording a comparison between cotton upon Avhich weevils 

 had been allowed to propagate without hindrance and other cotton,, 

 strictl}^ comparable, but from which the weevils had been practically 

 eliminated % poisoning, were summarized. It has generally been 

 found that the season's dusting upon any particular farm should 

 cost not to exceed the current value of 100 pounds of seed cotton per 

 acre, in order to make a profit by the dusting method. After making 

 all computations in this regard, the recommendation for dusting has 

 been modified to include all lands having a potential yield of over 

 one-third bale per acre and suffering fairly severe weevil infestation. 



The plat tests on methods of poisoning at Tallulah, La., have been 

 continued. The study on season of poisoning, with particular refer- 

 ence to comparisons between early and late-season applications, was 

 practically completed, and the results are being put into the form 

 of a bulletin for publication. 



The unusual interest in sweetened poisons for weevil control neces- 

 sitated carrying out large series of tests on this method, and many 

 such preparations were studied. So far the results have not been 

 sufficiently definite to warrant recommending the general use of such 

 preparations by planters, but the studies are being continued in the 

 hope of developing some way in which they can be used to advantage. 



The work in developing new t^'pes of equipment and improving 

 existing models has been continued. It has been found that as cotton 

 dusting extends to new districts, new problems of application from 



